 So that's an interesting question and something that's been troubling scientists for many years. What we can say is that we spend a third of our lives asleep. All living creatures sleep or have some kind of light-dark inactivity cycle from the smallest single-celled organism right up to ourselves. So you know from that that sleep is essential to health and well-being. It's evolved alongside us as we've evolved underneath the sun and those circadian rhythms are essential to the health and well-being of all living things. So sleep is clearly essential. There are many theories about why we sleep. None of them are completely either true or untrue but increasingly we're realizing the importance of sleep as an active dynamic process that makes sure that our wakeful hours are efficient and effective and makes sure that our body as well as our minds are performing optimally.